Book of Joel Chapter 2 Vs. 4

 The Day of the Lord

The appearance of them is as the appearance of horses; and as horsemen, so shall they run. Joel 2:4

The appearance of... The resemblance of the locust’s head to that of a horse is striking, so much so that the prophet reiterates the word appearance. Horses were not used for agricultural purposes in ancient times but were the most feared military equipment (Exo. 15:1, 19; Deut. 20:1; Jos. 11:4).

מַרְאֶה

mar'eh

mar-eh'

From H7200; a view (the act of seeing); also an appearance (the thing seen), whether (real) a shape (especially if handsome, comeliness; often plural the looks), or (mental) a vision: - X apparently, appearance (-reth), X as soon as beautiful (-ly), countenance, fair, favoured, form, goodly, to look (up) on (to), look [-eth], pattern, to see, seem, sight, visage, vision.

סֻס סוּס

sûs sûs

soos, soos

From an unused root meaning to skip (properly for joy); a horse (as leaping); also a swallow (from its rapid flight): - crane, horse ([-back, -hoof]). Compare H6571.

פָּרָשׁ

pârâsh

paw-rawsh'

From H6567, a steed (as stretched out to a vehicle, not single nor for mounting (compare H5483)); also (by implication) a driver (in a chariot), that is, (collectively) cavalry: - horseman.

כֵּן

kên

kane

From H3559; properly set upright; hence (figuratively as adjective) just; but usually (as adverb or conjugation) rightly or so (in various applications to manner, time and relation; often with other particles): - + after that (this, -ward, -wards), as . . . as, + [for-] as much as yet, + be (for which) cause, + following, howbeit, in (the) like (manner, -wise), X the more, right, (even) so, state, straightway, such (thing), surely, + there (where) -fore, this, thus, true, well, X you.

רוּץ

rûts

roots

A primitive root; to run (for whatever reason, especially to rush): - break down, divide speedily, footman, guard, bring hastily, (make) run (away, through), post, stretch out.

The simile continues with as of chariots (verse 5), Like a mighty people (verse 5), like mighty men (verse 7); and like soldiers (verse 7).

The noise these locusts would make would sound like many horse hooves. They can destroy an entire farm in just a few minutes.

Rev. 9:7 “And the shapes of the locusts [were] like unto horses prepared unto battle; and on their heads [were] as it were crowns like gold, and their faces [were] as the faces of men.”

In the context of the overall comparison to locusts, the invading force is likened to an army (Joel 2:5) consisting of horses… cavalry, and chariots (Joel 2:4-5). Such an association is facilitated by three facts: (1) The heads of locusts and horses are similar in appearance. The German and Italian words for locust literally mean hay-horse and little horse, respectively (Wolff, Joel and Amos, p. 45, n. 46; cf. also Driver, The Books of Joel and Amos, p. 52).